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Article

Oxygen Transport in YSZ∕LSM Composite Materials

[+] Author and Article Information
M. Dhallu, J. A. Kilner

 Department of Materials, Imperial College, London, SW7 2AZ, UK Tel: +44 207 589 5111 Ext. 56721manjit.dhallu@imperial.ac.uk

J. Fuel Cell Sci. Technol 2(1), 29-33 (Jul 30, 2004) (5 pages) doi:10.1115/1.1840840 History: Received March 24, 2004; Revised July 30, 2004

To date, a number of ceramic oxides with the perovskite structure have been proposed as membrane materials for the selective separation of oxygen and the partial oxidation of hydrocarbons due to their high oxygen permeation fluxes. In contrast, their instability under an oxygen pressure gradient and consequent lattice expansion has been shown to be the cause of their decomposition over time, thus generally limiting their use to oxidizing environments. This has led the search for possible materials to be diverted towards alternatives such as composites. In this work, we aim to further our understanding of oxygen transport in composite materials by continuing our studies on a model mixed conducting system of Zr0.84Y0.16O1.92 (YSZ) and (La0.8Sr0.2)0.98MnO3±δ (LSM) using the isotope exchange depth profiling method in conjunction with secondary ion mass spectrometry (SIMS). The measured effective tracer diffusion coefficients were in the range 108to107cm2s and the effective surface exchange coefficients in the range 108to105cms. The activation enthalpies for oxygen diffusion and surface exchange processes were calculated to be 113 and 318kJmol, respectively.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 5

Oxygen tracer diffusion coefficient data for LSM-YSZ composites as a function of inverse temperature at a nominal pressure of 200mbarO2. Data for 0 and 100wt% LSM adapted from Y. Ji (7).

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Figure 6

Oxygen surface exchange coefficient data for LSM-YSZ composites as a function of inverse temperature at a nominal pressure of 200mbarO2. Data for 0 and 100wt% LSM adapted from Y. Ji (7).

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Figure 4

Oxygen transport data for a LSM-YSZ (35:65wt%) composite as a function of inverse temperature at a nominal pressure of 200mbarO2. Lines are least squares fit to Arrhenius behavior.

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Figure 3

Typical O18 diffusion profile for a composite of LSM-YSZ (35:65wt%) annealed at 1179K for 5940s. Solid line shows fitting of data to diffusion model.

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Figure 2

Schematic illustration of O18 isotopic exchange technique for Line scanning mode of SIMS profiling. This mode is often utilized for measuring O18 penetration profiles for oxides with high diffusivity. Adapted from R. J. Chater (12).

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Figure 1

Calculated surface O18 fraction as function of the dimensionless variable h′

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